1. Technical Field
The present invention relates to a liquid-jet head and a liquid-jet apparatus, and more particularly, an ink-jet recording head and an ink-jet recording apparatus in which a part of a pressure generating chamber communicating with a nozzle orifice for ejecting ink droplets is constructed from a vibration plate, a piezoelectric element is formed on the surface of the vibration plate, and ink droplets are ejected by displacement of the piezoelectric element.
2. Related Art
In an ink-jet recording head, a part of a pressure generating chamber communicating with a nozzle orifice for ejection of ink droplets is composed of a vibration plate, and the vibration plate is deformed by a piezoelectric element to pressurize ink in the pressure generating chamber, thereby ejecting ink droplets from the nozzle orifice. Two types of the ink-jet recording heads are put into practical use. One of them uses a piezoelectric actuator in the longitudinal vibration mode which expands and contracts in the axial direction of the piezoelectric element. The other uses a piezoelectric actuator in the flexural vibration mode.
An example of the ink-jet recording head using the piezoelectric actuator in the flexural vibration mode is one in which a nozzle plate having nozzle orifices bored therein is joined to a surface of a passage-forming substrate having pressure generating chambers formed therein, and a reservoir forming plate having a reservoir portion provided to constitute a reservoir for storing ink to be supplied to each pressure generating chamber is joined to the other surface of the passage-forming substrate (see, for example, JP-A-2000-296616 (Claims, FIG. 2, etc.)).
In such an ink-jet recording head, the respective members are generally formed from different materials. Thus, the linear expansion coefficients of the respective members are different, posing the problem that peeling or delamination occurs between the respective members according to changes in the environmental temperature. With the structure of JP-A-2000-296616, for example, the passage-forming substrate and the reservoir forming plate comprise silicon plates or substrates, and their linear expansion coefficients are about 2.0 [×10−6/° C.], while the nozzle plate comprises stainless steel (SUS) and its linear expansion coefficient is 16 [×10−6/° C.]. As seen from these facts, the linear expansion coefficient greatly differs between the members. Therefore, if the head is placed at a temperature lower than the temperature during adhesion of the passage-forming substrate and the nozzle plate, the nozzle plate shrinks relatively, thereby generating shear stress between the plates, leading to the problem that delamination occurs between the passage-forming substrate and the reservoir forming plate.
Metal layers, such as a lower electrode and an upper electrode, on an elastic film are formed at high temperatures during sputtering, vapor deposition or the like, and thus have initial stress even at room temperature. That is, shear stress is generated between the elastic film and each metal layer. In the structure provided with a lead electrode, which is described in JP-A-2000-296616, for example, the adhered surface (its uppermost portion) on the elastic film is a wiring metal layer comprising gold (Au). Since the adhesiveness between the wiring metal layer and the adhesive agent is insufficient, the risk of delamination is high. When the temperature changes, tensile stress and shear stress in the film thickness direction due to warpage of the entire chip occur, so that a longitudinally end portion of the chip is at the highest risk of delamination.
Such problems are not limited to the ink-jet recording head for ejection of ink, but are similarly present in other liquid-jet heads for ejecting liquid droplets other than ink.